refactor: remove storage, backup, plugin/marketplace features

- Delete app/storage/ (blob_store, vector_store, encryption)
- Delete app/marketplace/ (plugin_registry, plugin_review, revenue_share)
- Delete routes: backup.py, plugins.py, storage.py, vectors.py
- Relocate embed endpoint to POST /chat/embed
- Rewrite migration 001 (remove storage/plugin tables)
- Delete migration 002 (seed_plugins)
- Remove S3/Pinecone/Qdrant env vars from settings
- Remove storage/backup quotas from tier_manager
- Remove MinIO and Qdrant from docker-compose
- Delete tests: test_backup, test_plugins, test_storage
- Update README.md and clean .env.example

.env.example

@@ -23,21 +23,6 @@ LLM_ROUTER_MODEL=gpt-4o-mini
 STRIPE_SECRET_KEY=
 STRIPE_WEBHOOK_SECRET=
 
-# ── AWS / S3 ──────────────────────────────────────────────────────────────────
-S3_BUCKET=adiuva
-S3_REGION=us-east-1
-S3_ENDPOINT_URL=
-AWS_ACCESS_KEY_ID=
-AWS_SECRET_ACCESS_KEY=
-# For MinIO (homelab): S3_ENDPOINT_URL=http://minio:9000
-
-# ── Vector Store ──────────────────────────────────────────────────────────────
-# Pinecone is used when PINECONE_API_KEY is set; otherwise falls back to Qdrant.
-PINECONE_API_KEY=
-PINECONE_INDEX=adiuva
-QDRANT_URL=
-QDRANT_API_KEY=
-# For local Qdrant (homelab): QDRANT_URL=http://qdrant:6333
 
 # ── Langfuse (leave empty to disable observability) ───────────────────────────
 LANGFUSE_SECRET_KEY=